1. Field of the Invention
The present invention relates to a lens array unit and a process for making a lens array. A lens array or a lens array unit is incorporated in an optical apparatus such as an image reading apparatus for converging light from an object (e.g. document) to form an image of the object at a predetermined position (e.g. on a light receiving element).
2. Description of the Related Art
In an image reading apparatus such as a facsimile machine or a scanner, a plurality of light receiving elements arranged in a line are utilized to read an image of an object in a non-inverted, non-magnified manner. In this case, image forming means need be provided between the document and the plurality of light receiving elements to form an actual size erect image of the object on the plurality of light receiving elements. The image forming means may be a lens array unit. A lens array unit consists of a plurality of lens arrays stacked on each other, where each array has two opposite surfaces in which a plurality of convex lens faces are integrally formed (See FIGS. 1 and 2).
The lens array unit may be made by cutting out several lens arrays from a resin casting provided with lens array-forming regions (see FIG. 5) and then connecting two lens arrays, for example.
For cutting out lens arrays from a resin casting, use may be made of a laser beam cutting method or ultrasonic vibration cutting method. However, when the resin casting is formed of PMMA for example, laser beams will simply pass through the resin casting, thereby making no cuts in the resin casting. With the ultrasonic vibration cutting method, on the other hand, the cut portion will melt or become soft as in a case where thermal energy is applied to the resin casting. This may leads to problems that the cut surface cannot be made a mirror surface, and that cut burrs may be left on the cut surface. In such adverse circumstances, dust may adhere to the cut surface, the burrs, or even onto the lens face. It is probable that the burr itself may adhere to the lens face in assembling the lens array or incorporating the lens array in an image reading apparatus. In this situation, the optical performance of the lens unit will deteriorate.
As an alternative method, use may be made of a rotary cutter designed for cutting lens arrays one by one out of the resin casting. However, this one-cutter method provides poor work efficiency. Another problem is caused when the rotary cutter is about to make a second cut in the resin casting after a first cut has been made. Specifically, while the second cut is being made, the rotary cutter gives pressure to the lens array region, thereby causing the region to warp into the space of the first cut. In this situation, the resultant cut surface fails to be straight and cannot be made a mirror surface. Unfavorably, this may deteriorate the optical performance of the lens array.
Turning now to a method of assembling lens arrays, a first lens array may be formed with projections, while a second lens array may be formed with recesses into which the projections of the first lens array are fitted. To secure the attachment, adhesive may be applied to the engaging portions.
However, when there is a large dimensional error in the projections or holes mentioned above, the projections fail to be properly fitted into the holes. In this situation, the connected lens arrays fail to be parallel to each other, or the lenses of the respective arrays are unaligned, or the distance between the connected lens arrays is unduly greater or smaller than the design value.
These problems may occur in using adhesive for the projections and the holes, unless the amount of the adhesive is suitably controlled. When too much adhesive is applied, the adhesive may be pressed out of the engaging holes and flow onto a nearby lens. Unfavorably this causes the optical properties of the lens to vary. In particular, when the adhesive is the so-called instantaneous type, the lens properties may be significantly changed due to the whitening of the hardening adhesive.
It is an object of the present invention to provide a technique enabling easy manufacture of a lens array and lens array unit having a good optical performance.
According to a first aspect of the present invention, there is provide a process for making a lens array unit. In a lens array forming step, a first lens array including a plurality of first lenses arranged in a line and a second lens array including a plurality of second lenses arranged in a line are formed. In a lens array connecting step, the first lens array is connected to the second lens array so that a lens axis of each of the first lenses is aligned with a lens axis of a corresponding one of the second lenses. The lens array connecting step includes supplying of ultrasonic vibration.
Preferably, one of the first and the second lens arrays is provided with a male part whereas the other of the lens arrays is provided with a female part. In the lens array connecting step, the male part is incompletely or provisionally fitted into the female part to provide a provisional assembly, and ultrasonic vibration is supplied to the provisional assembly for melting an obverse surface of the male part and/or an inner surface of the female part so as to completely fit the male part into the female part.
The obverse surface of the male part or the inner surface of the female part may be provided with a projection for concentrating ultrasonic energy in supplying the ultrasonic vibration.
The lens array unit may further comprise a light-shielding member formed with a plurality of through-holes, where each of the through-holes is positioned in facing relation to a corresponding one of the first lenses. In the lens array connecting step, it is preferable that the light-shielding member is connected to the first lens array utilizing the ultrasonic vibration supplied for ultrasonically welding the first lens array to the second lens array.
Preferably, the light-shielding member may be different in material from the first lens array.
Preferably, one of the first lens array and the second lens array may be provided with a stopper for engaging the other lens array when the male part is fitted into the female part.
The male part may include a first taper surface and the female part may include a second taper surface for engaging the first taper surface when the male part is provisionally fitted into the female part.
Preferably, measurements are made in advance with respect to variation of a distance between the first lens array and the second lens array after the ultrasonic vibration supply is started, and the ultrasonic vibration supply is stopped in the measured period of time during which the above-mentioned distance is constant.
The ultrasonic vibration may be supplied with an ultrasonic horn, arranged to generate longitudinal vibration. The horn is pressed against an ultrasonic supply surface of the provisional assembly. The ultrasonic vibration supplied to the ultrasonic supply surface may have a frequency of 10-30 kHz and a total energy of 20-40 J.
The lens array forming step may be performed by cutting the first lens array or the second lens array out of a resin casting formed with a plurality of lens array regions. Each of the lens array regions is formed with a plurality of first lenses or second lenses arranged in a line, and the plurality of lens array regions are aligned with each other in a direction transverse to the line of the first lenses or the second lenses.
In cutting out the first lens array or the second lens array, use may be made of a multiple-blade rotary cutter including a plurality of rotary blades regularly spaced from each other at a pitch corresponding to a dimension of each of the lens array regions in the transverse direction. With the use of the cutter, slits are formed simultaneously at sides of the lens array regions.
The forming of the slits may include a first step of cutting the resin casting from a first surface of the resin-mold article with a plurality of first rotary blades to form a plurality of first grooves extending to an intermediate point of a thickness of the resin casting, and a second step performed after the first step for cutting the resin casting from a second surface opposite the first surface with a plurality of second rotary blades which are thicker than the first rotary blades to form a plurality of second grooves connected to the first grooves to provide the slits.
Preferably, the first and the second steps may be performed to satisfy the inequalities of
t1 greater than t/2, t2 greater than (txe2x88x92t1), t2 less than t/2
where t1 is a depth of each of the first grooves before the second step is performed, t2 is a depth of each of the second grooves and t is a thickness of the resin casting at the sides of the plurality of lens array regions.
For example, the lens array unit may serve as image forming means in an optical apparatus for converging light traveling from an object for forming an image of the object at a predetermined position.
According to a second aspect of the present invention, there is provided a process for making a lens array unit comprising a lens array forming step for forming a lens array including a plurality of lenses arranged in a line, and a light-shielding member connecting step for connecting a light-shielding member formed with a plurality of through-holes arranged in a line to the lens array so that each of the through-holes is positioned in facing relationship to a corresponding one of the lenses. The light-shielding member connecting step includes supplying of ultrasonic vibration.
Preferably, one of the lens array and the light-shielding member may be provided with a male part whereas the other one may be provided with a female part. In the light-shielding member connecting step, the male part is provisionally fitted into the female part to provide a provisional assembly, and the ultrasonic vibration is supplied to the provisional assembly for melting and softening at least one of an obverse surface of the male part and an inner surface of the female part for completely fitting the male part into the female part. Preferably, measurement is performed in advance with respect to variation of a distance between the lens array and the light-shielding member after the ultrasonic vibration supply is started, and the ultrasonic vibration supply is stopped in the measured period of time during which the above-mentioned distance is constant.
Preferably, the male part may include a first taper surface and the female part may include a second taper surface for engaging the first taper surface when the male part is provisionally fitted into the female part.
Preferably, the light-shielding member may be different in material from the lens array. The ultrasonic vibration may be supplied from an ultrasonic horn, capable of supplying longitudinal vibration. The horn is pressed against an ultrasonic supply surface of the provisional assembly. The ultrasonic vibration supplied to the ultrasonic supply surface may have a frequency of 10-30 kHz and a total energy of 20-40 J.
According to a third aspect of the present invention, there is provided a process for making a lens array unit comprising a lens array forming step for forming a first lens array including a plurality of first lenses arranged in a line and a second lens array including a plurality of second lenses arranged in a line. The process also comprises a lens array connecting step for connecting the first lens array to the second lens array so that a lens axis of each of the first lenses is aligned with a lens axis of a corresponding one of the second lenses. The lens array forming step includes cutting the first lens array or the second lens array out of a resin casting formed with a plurality of lens array regions. Each of the lens array regions is formed with a plurality of first lenses or second lenses arranged in a line, and the plurality of lens array regions are aligned with each other in a direction transverse to the line of the first lenses or the second lenses. In the cutting of the first lens array or the second lens array, slits are formed simultaneously at sides of the lens array regions using a multiple-blade rotary cutter including a plurality of rotary blades regularly spaced from each other at a pitch corresponding to a dimension of each of the lens array regions in the transverse direction.
The forming of the slits includes a first step of cutting the resin casting from a first surface of the resin casting with a plurality of first rotary blades to form a plurality of first grooves extending to an intermediate point of a thickness of the resin casting, and a second step performed after the first step for cutting the resin casting from a second surface opposite the first surface with a plurality of second rotary blades which are thicker than the first rotary blades to form a plurality of second grooves connected to the first grooves to provide the slits. Preferably, the first and the second steps are performed to satisfy the inequalities of
t1 greater than t/2, t2 greater than (txe2x88x92t1), t2 less than t/2
where t1 is a depth of each of the first grooves before the second step is performed, t2 is a depth of each of the second grooves and t is a thickness of the resin casting at the sides of the plurality of lens array regions.
For example, the resin casting includes a plurality of first lens array regions and the same number of second lens array regions. Each of the first lens array regions later becomes a first lens array while each of the second lens array regions later becomes a second lens array. In the lens array forming step, plural pairs of a first lens array and a second lens array are obtained from one resin casting. Preferably, in the lens array connecting step, the first lens array is connected to the second lens array simultaneously with respect to the plural pairs.
According to a second aspect of the present invention, there is provided a process for making a lens array comprising the steps of: preparing a resin casting integrally formed with a plurality of lens array regions each of which includes a plurality of lenses arranged in a line, the plurality of lens array regions being aligned with each other in a direction transverse to the line of the plurality of lenses; and forming slits simultaneously at sides of the lens array regions using a multiple-blade rotary cutter including a plurality of rotary blades regularly spaced from each other at a pitch corresponding to a dimension of each of the lens array regions in the transverse direction.
Preferably, the step of forming slits may be performed while cooling the resin casting. The cooling of the resin casting may be performed by supplying cooling water to a contact area between the multiple-blade rotary cutter and the resin casting and to an area adjacent to the contact area.
The forming of the slits may includes a first step of cutting the resin casting from a first surface of the resin casting with a plurality of first rotary blades to form a plurality of first grooves extending to an intermediate point of a thickness of the resin casting, and a second step performed after the first step for cutting the resin casting from a second surface opposite the first surface with a plurality of second rotary blades which are thicker than the first rotary blades to form a plurality of second grooves connected to the first grooves to provide the slits. Preferably, the first and the second steps may be performed to satisfy the inequalities of
t1 greater than t/2, t2 greater than (txe2x88x92t1), t2 less than t/2
where t1 is a depth of each of the first grooves before the second step is performed, t2 is a depth of each of the second grooves and t is a thickness of the resin casting at the sides of the plurality of lens array regions.
For example, the resin casting may be 0.8-2.0 mm in thickness, the multiple-blade rotary cutter may be moved at a velocity of 500-2,000 mm/min, and each of the rotary blades is driven at a rotation speed of 2,000-6,000 rpm.
Each of the rotary blades may be 50-150 mm in diameter and has sawteeth the number of which is from 100 to 200.
According to a fifth aspect of the present invention, there is provided a process for making a lens array comprising the steps of: preparing a resin casting integrally formed with a plurality of lens array regions each of which includes a plurality of lenses arranged in a line, the plurality of lens array regions being aligned with each other in a direction transverse to the line of the plurality of lenses; and forming slits at sides of the lens array regions. The forming of the slits includes a first step of cutting the resin casting from a first surface of the resin-mold article with a plurality of first rotary blades to form a plurality of first grooves extending to an intermediate point of a thickness of the resin casting, and a second step performed after the first step for cutting the resin casting from a second surface opposite the first surface with a plurality of second rotary blades which are thicker than the first rotary blades to form a plurality of second grooves connected to the first grooves to provide the slits.
Preferably, the first and the second steps may be performed to satisfy the inequalities of
t1 greater than t/2, t2 greater than (txe2x88x92t1), t2 less than t/2
where t1 is a depth of each of the first grooves before the second step is performed, t2 is a depth of each of the second grooves and t is a thickness of the resin casting at the sides of the plurality of lens array regions.